1. Field of the Invention
The present invention relates to a bulk battery or thin film battery, and a fabrication method thereof, and in particular to an improved battery which can increase an amount of an electrode and contact area between the electrode and an electrolyte per unit battery area by forming trenches on a substrate where a cathode is formed or on each thin film element sequentially formed on the substrate, and by increasing an effective area per unit area.
2. Description of the Background Art
Recently, a secondary battery has been studied as a power source of portable electric devices or microelectronic devices. As electric devices have become smaller, the size of the batteries have also become smaller, and the performance of the batteries have improved. It is expected that the secondary battery may extensively adapt to most kinds of the micro-electronic devices as well as light-weight mobile communication devices (for example, cellular phones) or portable computers. As the micro-electronic devices gradually consume less power, the conventional thin film battery structure (U.S. Pat. No. 5,338,625) may be adapted to various fields. According to a research result on secondary batteries, the battery has very stable operational properties and can be reduced in size. Also, it is possible to fabricate the battery in a small size by using a semiconductor process. The thin film battery which is one of the small size batteries is not restricted in shape or size. Therefore, when used as a power source for a device, the thin film battery can be fabricated in a comparatively small size, and thus can be adapted to the micro-electronic devices.
The performance of the battery is decided by current density, a total current storage density and a charging speed. When the thin film battery is applied to light-weight mobile communication devices, portable computers and micro-electromechanical systems requiring a comparatively high consumption power, the most difficult points are that the current density and the total current storage density are lowered due to a property of a thin film. Accordingly, in order to apply the light-weight thin film battery which can be fabricated in various shapes to devices having a comparatively high consumption power and current density, the total current storage density of the thin film battery must be increased. The total current storage density is decided by an amount of an electrode (cathode) and electrode materials used. The electrode materials which have been generally employed are LiCoO2, V2O2, LiMnO2 and LiNiO2. Although each material has the total current storage density of a theoretical value, the completed thin film battery has a current storage density lower than the theoretical value. In order to increase an amount of the electrode to improve the total current storage density, in the case the electrode material is deposited thick, an internal resistance of the thin film battery is increased, and thus a voltage thereof is dropped. As a result, so as to increase the amount of the electrode, it is necessary to increase a contact area between the electrode and an anode per unit battery area.
FIG. 1 is a cross-sectional view illustrating a conventional thin film battery. As shown therein, a contact interface area among a first collector 1, a cathode 2 and an electrolyte 3 of the thin film battery is identical to an effective area of the battery. The amount of the electrode, namely the thickness of the cathode 2 is limited by an increase of the internal resistance. Therefore, the total current storage density also has a limited value. In addition, the charging speed is determined by the interface area among the first collector 1, the cathode 2, the electrolyte 3, the anode 4 and the second collector 6. Here, the collectors 1, 6 denote conductive materials.
Accordingly, it is an object of the present invention to provide a battery which has an improved performance by providing a trench structure to thin film elements, by increasing a size of an effective area per unit area of each thin film element, and by considerably increasing an amount of an electrode (cathode) and a contact area among a collector, an electrode and an electrolyte per unit battery area. The trench structure is adaptable to a bulk battery as well as the thin film battery.
In order to overcome disadvantages of the conventional art in a battery area and an interface area of each thin film element composing a battery, in accordance with the present invention, a trench structure is applied to a thin film battery consisting of a substrate, a first collector, a cathode, an electrolyte, an anode and a second collector. According to the present invention, the trenches are formed by etching the respective thin film elements which are sequentially stacked, namely the substrate, the first collector or the cathode. In addition, the trench structure can be applied to the bulk battery. In fabricating the thin film battery having the trench structure, a planarization process may performed after forming the anode, and a step of forming an encapsulation film on the anode may be further included.